The present invention relates generally to storage systems and specifically to file migration in hierarchical storage systems.
Hierarchical storage systems support migration operations that transfer data from a primary storage device to a secondary storage device and recall operations that transfer data from a secondary storage device to a primary storage device. While migration operations may be conducted as a background process well after a client writes the data to the primary storage device, recall operations are preferably conducted immediately in order to provide a timely response to the client that needs to access the data.